Progressive rate leaf spring for vehicle suspension system

ABSTRACT

A variable rate leaf spring vehicle suspension system includes a vehicle frame. The suspension system also includes a single leaf spring extending from a first end to a second end. The suspension system further includes a tension shackle pivotably coupled to the vehicle frame about an axis, the tension shackle defining a channel, the second end of the leaf spring disposed within the channel of the tension shackle, wherein the axis about which the tension shackle is pivotable is below the second end of the leaf spring.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. patent application Ser. No.16/793,477, filed Feb. 18, 2020, which claims priority to U.S.Provisional Patent Application No. 62/807,519, filed on Feb. 19, 2019,the disclosures of which are each incorporated by reference herein intheir entireties.

FIELD OF THE INVENTION

This invention relates generally to leaf spring suspension systems forvehicles.

BACKGROUND

Leaf spring systems have for many years been used for the suspension ofwheeled vehicles. The central element of a leaf spring suspension systemfor a vehicle is termed a “semi-elliptical” spring configured as anarc-shaped length of spring steel having a substantially rectangularcross-section. At the center of the arc is provided an arrangement forcoupling to the axle of the vehicle. At the ends are provided couplerholes for attaching the spring to the vehicle body. For heavy vehicles,leaf springs are stacked on one another to form layers of springs ofdifferent lengths. Leaf springs are still used in heavy commercialvehicles and railway carriages. In the case of very heavy vehicles, leafsprings provide the advantage of spreading the load over a larger regionof the vehicle's chassis. A coil spring, on the other hand, willtransfer the load to a single point. Unfortunately, typical steel leafspring arrangements are heavy.

Some spring arrangements include features that provide a multi-platearrangement with a multi-stage spring rate that dictates, in part, theresponse to certain driving maneuvers that is felt by an occupant of thevehicle. The multi-plate, multi-stage spring rate designs often sufferfrom abrupt changes that are felt by the user in an undesirable manner.

SUMMARY OF THE INVENTION

According to an aspect of the disclosure, a variable rate leaf springvehicle suspension system includes a vehicle frame. The suspensionsystem also includes a single leaf spring extending from a first end toa second end. The suspension system further includes a tension shacklepivotably coupled to the vehicle frame about an axis, the tensionshackle defining a channel, the second end of the leaf spring disposedwithin the channel of the tension shackle, wherein the axis about whichthe tension shackle is pivotable is below the second end of the leafspring.

According to another aspect of the disclosure, a variable rate leafspring vehicle suspension system includes a vehicle frame. Thesuspension system also includes a single leaf spring extending from afirst end to a second end. The suspension system further includes atension shackle pivotably coupled to the vehicle frame about an axis,the tension shackle defining a channel, the second end of the leafspring disposed within the channel of the tension shackle, whereinpivoting of the tension shackle in response to an increasing, upwardload reduces the effective length of the leaf spring.

According to yet another aspect of the disclosure, a variable rate leafspring vehicle suspension system includes a vehicle frame. Thesuspension system also includes a first leaf spring extending from afirst end to a second end. The suspension system further includes asecond leaf spring extending from a third end to a fourth end. Thesuspension system yet further includes a tension shackle pivotablycoupled to the vehicle frame about an axis, the tension shackle defininga channel, the second end of the first leaf spring disposed within thechannel of the tension shackle, wherein the axis about which the tensionshackle is pivotable is below the second end of the first leaf spring.The suspension system also includes a first bumper disposed between atop surface of the first leaf spring and the vehicle frame. Thesuspension system further includes a second bumper disposed between atop surface of the second leaf spring and a bottom surface of the firstleaf spring, the second bumper spaced from the first leaf spring in afirst load condition of the second leaf spring and configured to providea first overall spring rate, and in contact with the first leaf springin a load second condition of the second leaf spring, contact betweenthe second bumper and the first leaf spring configured to provide asecond overall spring rate, the first bumper spaced from the vehicleframe in a third load condition of the second leaf spring and configuredto provide a third overall spring rate, and in contact with the vehicleframe in a fourth load condition of the second leaf spring, contactbetween the first bumper and the vehicle frame configured to provide afourth overall spring rate.

These and other advantages and features will become more apparent fromthe following description taken in conjunction with the drawings

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of a vehicle suspension system;

FIG. 2 is a side, elevational view of a leaf spring of the vehiclesuspension system according to an embodiment;

FIG. 3 is a side, elevational view of a first end of the leaf spring ofFIG. 2 having a bumper thereon;

FIG. 4 is a side, elevational view of a second end of the leaf spring ofFIG. 2 disposed in a tension shackle;

FIG. 5 is a side, elevational view of the leaf spring of FIG. 2deflecting during operation;

FIG. 6 is a perspective view of the second end of the leaf spring ofFIG. 2 deflecting during operation;

FIG. 7 is a side, elevational view of a leaf spring of the vehiclesuspension system according to another embodiment;

FIG. 8 is a perspective view of a second end of the leaf spring of FIG.7 disposed in a compression shackle;

FIG. 9 is a side, elevational view of the leaf spring of FIG. 7;

FIG. 10 is side, elevational view of the leaf spring of FIG. 7deflecting during operation; and

FIG. 11 is a plot of rate of the leaf spring against deflectioncomparing the leaf spring disclosed herein vs. a typical steel springarrangement.

DETAILED DESCRIPTION

Referring to FIG. 1, illustrated is a vehicle suspension system 10having a chassis generally designated with numeral 12. The chassis 12includes a first chassis rail 14 and a second chassis rail 16 that arearranged substantially parallel to each other. The first and secondchassis rails 14, 16 are coupled to each another by at least one crossbrace, such as a first cross brace 18 and a second cross brace 20, asshown. A differential drive arrangement 22 is fixedly coupled to thechassis 12 and converts the rotary motion of a drive shaft (not shown)to substantially orthogonal rotary motion at axle 24. The axle 24includes an associated pair of universal joints (not specificallydesignated) that are arranged to be proximal and distal with respect tothe differential drive arrangement 22. Thus, the axle 24 has anassociated longitudinal axis to accommodate transaxial motion. It is tobe appreciated that the axle 24 refers to a pair of half shafts in someembodiments. The half shafts may be disposed within a single sleeve oruncovered.

A leaf spring 32 is operatively coupled at a first end 33 and a secondend 35 to the chassis rail 14. In some embodiments, the leaf spring 32is operatively coupled, at least in part, to the chassis rail 14 with aneye spring bushing arrangement 41 at the first end 33. For purposes ofdiscussion, only leaf spring 32 has been described in detail, but it isto be appreciated that a corresponding leaf spring is located on anopposing side of the chassis 12 proximate chassis rail 14.

The above-described spring 32 may be referred to as a “semi-elliptical”spring configured as an arc-shaped length segment. The spring is formedof a composite material to reduce the weight of the leaf spring 32 insome embodiments. However, it is to be appreciated that spring 32 may beformed of steel in other embodiments.

Referring now to FIG. 2, a first embodiment of the leaf spring 32 isillustrated in greater detail. Disposed between the first end 33 and thesecond end 35 of the leaf spring 32 is a retention assembly 34 tooperatively couple (directly or indirectly) the leaf spring 32 to theaxle 24. The retention assembly 34 may be a cage U-bolt plate, or anyother suitable structure for operatively coupling the leaf spring 32 tothe axle 24. A bumper 36 is located proximate the first end 33 of theleaf spring 32. The bumper 36 may be operatively coupled to, orintegrally formed with, the eye spring bushing arrangement 41 (asillustrated) or the leaf spring 32 itself. Location of the bumper 36being proximate to the first end 33 of the leaf spring 32 is defined bythe bumper 36 being located closer to the first end 33 relative to adistance between the bumper 36 and a mid-point of the leaf spring 32.The bumper 36 may be formed of any suitable resilient material,including a polymeric material or rubber, for example.

FIG. 3 illustrates the first end 33 of the leaf spring 32 in greaterdetail. The bumper 36 is positioned on a top side of the eye springbushing arrangement 41 to contact the frame (e.g., chassis rail 14)during vertical deflections of the leaf spring 32 in response to variousmovements of the vehicle, such as acceleration, braking, lateralmovement due to turning maneuvers, movement due to changing roadsurfaces, etc. It is contemplated that the bumper 36 is disposed onanother structure that the leaf spring 32 is engaged with, or even theleaf spring 32 itself. The bumper 36 is shown in close proximity to, orengagement with, the chassis rail 14 in FIG. 3. The resilient materialof the bumper 36 softens the engagement of the bumper (and therefore theeye spring 41 and leaf spring 32) with the vehicle frame.

Referring again to FIG. 2, as well as FIG. 4, the second end 35 of theleaf spring 32 is disposed within a channel 37 defined by a tensionshackle 38 that is coupled to a portion of the vehicle frame, such aschassis rail 14. The tension shackle 38 is pivotably coupled to thevehicle frame about axis A in any suitable manner. In the illustratedembodiment, the tension shackle 38 includes a first leg 40 and a secondleg 42 that are spaced from each other to define channel 37. The channel37 is dimensioned to effectively clamp the second end 35 of the leafspring 32 therein.

Engagement of the bumper 36 with the chassis rail 14 in response tospring deflection relative to chassis rail 14 initiates a second springrate of the leaf spring 32 to provide desirable spring characteristicsthat facilitate specified suspension dynamics. The precise location ofthe bumper 36 along the length of the leaf spring 32 may be adjusted todetermine how much spring deflection is required before contact betweenthe bumper 36 and the chassis rail 14 occurs. Additionally, the tensionshackle 38 that clamps the second end 35 of the leaf spring 32 allowsthe “effective length” of the leaf spring 32 to be further shortened,thereby increasing the spring rate of leaf spring 32 during deflection.Reducing the effective length of the leaf spring 32 refers to changingthe fulcrum location of the leaf spring 32 from outermost ends to adifferent (i.e., inward) location.

The tension shackle 38 pivots about axis A during deflection of the leafspring, as shown in FIG. 4, to gradually decrease the effective lengthof the leaf spring 32, thereby increasing the rate of the leaf spring32. With the bumper 36 and the tension shackle 38, each side 33, 35 ofthe leaf spring 32 provides parameters to adjust the rate progressionwithout having to change the curvature or thickness profile of the leafspring 32. By controlling the engagement of the bumper 36 and parametersof the tension shackle 38, the seat angle of the leaf spring 32 can beadjusted to a desired direction. The height of the bumper 36 andresiliency of the bumper material are factors that facilitatecustomization of the rate progression. Regarding the tension shackle 38,the radius R defined by the distance between axis A and arc length C(FIG. 4), as well as the clamp length L, similarly facilitatescustomization. An additional customization parameter is defined by theangle between axis A and the portion of arc length C that is along theleaf spring 32. FIGS. 5 and 6 illustrate the leaf spring 32 duringdeflection.

Referring now to FIG. 7, as with the embodiments of FIGS. 2-6, the firstend 33 of the leaf spring 32 includes a bumper 36 is positioned on a topside of the eye spring bushing arrangement 41 to contact the frame(e.g., chassis rail 14) during vertical deflections of the leaf spring32 in response to various movements of the vehicle, such asacceleration, braking, lateral movement due to turning maneuvers,movement due to changing road surfaces, etc. It is contemplated that thebumper 36 is disposed on another structure that the leaf spring 32 isengaged with, or even the leaf spring 32 itself. The bumper 36 is shownspaced from the vehicle frame in FIG. 7 and in close proximity to, orengagement with, the chassis rail 14 in FIG. 10. The resilient materialof the bumper 36 softens the engagement of the bumper (and therefore theeye spring 41 and leaf spring 32) with the vehicle frame.

Referring now to FIGS. 8-10, with continued reference to FIG. 7, thesecond end 35 of the leaf spring 32 is disposed within a channel 137defined by a compression shackle 138 that is coupled to a portion of thevehicle frame, such as chassis rail 14. The compression shackle 138 iscoupled to the vehicle frame in any suitable manner. In the illustratedembodiment, the compression shackle 138 includes a first portion 140that defines channel 137. The channel 137 is dimensioned to effectivelyclamp the second end 35 of the leaf spring 32 therein.

Engagement of the bumper 36 with the chassis rail 14 in response tospring deflection relative to chassis rail 14 initiates a second springrate of the leaf spring 32 to provide desirable spring characteristicsthat facilitate specified suspension dynamics. The precise location ofthe bumper 36 along the length of the leaf spring 32 may be adjusted todetermine how much spring deflection is required before contact betweenthe bumper 36 and the chassis rail 14 occurs. Additionally, thecompression shackle 138 that clamps the second end 35 of the leaf spring32 allows the “effective length” of the leaf spring 32 to be furthershortened, thereby increasing the spring rate of leaf spring 32 duringdeflection. Reducing the effective length of the leaf spring 32 refersto changing the fulcrum location of the leaf spring 32 from outermostends to a different (i.e., inward) location.

The compression shackle 138 includes the above-noted first portion 140which defines the channel 137. A shackle bumper 141 is operativelycoupled to a top side of the first portion 140 of the compressionshackle 138. As with bumper 36, the shackle bumper 141 may be formed ofany suitable resilient material, including a polymeric material orrubber, for example. A second portion 142 of the compression shackle 138is coupled to the first portion 140 in a manner that allows relativerotation of the first and second portions 140, 142. The second portion142 includes a contact member 144 that is positioned to contact theshackle bumper 141 after sufficient deflection of the leaf spring 32during operation.

Contact of the bumper 36 and/or the shackle bumper 141 during deflectionof the leaf spring, as shown in FIG. 10, gradually decreases theeffective length of the leaf spring 32, thereby increasing the rate ofthe leaf spring 32. With the bumper 36 and the compression shackle 138,each side 33, 35 of the leaf spring 32 provides parameters to adjust therate progression without having to change the curvature or thicknessprofile of the leaf spring 32. By controlling the engagement of thebumper 36 and parameters of the compression shackle 138, the seat angleof the leaf spring 32 can be adjusted to a desired direction. The heightof bumper 36 and/or shackle bumper 141, and resiliency of the materialof the bumpers are factors that facilitate customization of the rateprogression. Regarding the compression shackle 138, the radius ofcurvature, as well as the clamp length L, and position of contactbetween the shackle bumper 141 and the contact member 144 similarlyfacilitates customization.

It is further contemplated in another aspect of the invention that asecond leaf spring is provided, with the additional leaf spring clampedto the leaf spring 32 with the retention assembly 34 in a stackedarrangement. Any of the previously described embodiments may be utilizedwith the stacked arrangement described herein. The additional leafspring does not extend a distance that spans an entirety of the leafspring 32 in some embodiments. Bumpers may be fixed to the additionalleaf spring proximate ends thereof on a side of the additional leafspring that is adjacent the leaf spring 32. In a relaxed condition ofthe leaf spring arrangement, the bumpers are spaced from the leaf spring32.

Engagement of one or both of the bumpers with the leaf spring 32 inresponse to spring deflection initiates a third spring rate of the leafspring arrangement to provide desirable spring characteristics thatfacilitate specified suspension dynamics. The precise location of thebumpers along the length of the additional leaf spring may be adjustedto determine how much spring deflection is required before contactbetween the bumpers and the leaf spring 32 occurs. Initiation of thethird spring rate of the additional leaf spring may be adjusted based onthe location of the bumpers. As with the bumpers of the leaf spring 32,such an arrangement provides flexibility of the spring responsecharacteristics, while avoiding the need for a second leaf springarrangement, thereby reducing the weight of the suspension system 10 andthe overall vehicle.

The order of engagement of the bumpers 36, 141 of the leaf spring 32with the chassis rail 14 relative to engagement of the additional leafspring bumpers with the leaf spring 32 may be adjusted to control thespring response characteristics. In other words, bumpers of leaf spring32 engage the chassis rail 14 prior to engagement of the bumpers of theadditional leaf spring with the leaf spring 32 in some embodiments. Inother embodiments, additional leaf spring bumpers engage the leaf spring32 prior to engagement of the bumpers of leaf spring 32 with the chassisrail 14 in some embodiments. The use of the bumpers at the eye springarrangement location avoids undesirable contact and rubbing ofcomponents with the composite material. Such contact and rubbing isdetrimental to a composite spring and is a consideration that is not ofconcern to steel spring arrangements. It is to be appreciated that themulti-spring arrangement embodiments described herein may includesprings that are each formed of steel, each formed of a composite, or acombination thereof. For example, in a two-spring arrangement, a mainspring plate may be formed of steel, while a secondary spring plate maybe formed of a composite material, or vice versa. Alternatively, themain spring plate and the secondary spring plate may be both formed ofsteel. Another alternative includes a main spring plate and a secondaryspring plate that are both formed of a composite material. It is easilyunderstood that the above-described example may be carried on to threeor more spring arrangements.

FIG. 11 illustrations a plot of rate of the leaf spring againstdeflection comparing the leaf spring disclosed herein vs. a typicalsteel spring arrangement. In particular, curve 200 depicts the ratechange of the leaf spring 32 disclosed herein, when used in conjunctionwith the tension shackle or the compression shackle. The curve 200 issmooth when compared to the steep jump in rate change associated withprior multi-plate, multi-stage spring designs (represented with line202).

Although the invention has been described in terms of specificembodiments and applications, persons skilled in the art may, in lightof this teaching, generate additional embodiments without exceeding thescope or departing from the spirit of the invention described herein.Accordingly, it is to be understood that the drawing and description inthis disclosure are proffered to facilitate comprehension of theinvention, and should not be construed to limit the scope thereof

Having thus described the invention, it is claimed:
 1. A variable rateleaf spring vehicle suspension system comprising: a vehicle frame; asingle leaf spring extending from a first end to a second end; and atension shackle pivotably coupled to the vehicle frame about an axis,the tension shackle defining a channel, the second end of the leafspring disposed within the channel of the tension shackle, wherein theaxis about which the tension shackle is pivotable is below the secondend of the leaf spring.
 2. The system of claim 1, further comprising aneye spring bushing coupled to the vehicle frame, the first end of theleaf spring coupled to the eye spring bushing.
 3. The system of claim 2,further comprising a bumper operatively coupled to, or integrally formedwith, the eye spring bushing and disposed between the eye spring bushingand the vehicle frame, the bumper spaced from the vehicle frame in afirst condition of the leaf spring and configured to provide a firstspring rate, and in contact with the vehicle frame in a second conditionof the leaf spring, contact between the bumper and the vehicle frameconfigured to provide a second spring rate of the leaf spring.
 4. Thesystem of claim 3, wherein the bumper is formed of a polymeric material.5. The system of claim 1, further comprising a bumper operativelycoupled to, or integrally formed with, the first end of the leaf springand disposed between the leaf spring and the vehicle frame, the bumperspaced from the vehicle frame in a first condition of the leaf springand configured to provide a first spring rate, and in contact with thevehicle frame in a second condition of the leaf spring, contact betweenthe bumper and the vehicle frame configured to provide a second springrate of the leaf spring.
 6. The system of claim 1, wherein the singleleaf spring is formed of a composite material. The system of claim 1,wherein the single leaf spring is formed of metal.
 8. A variable rateleaf spring vehicle suspension system comprising: a vehicle frame; asingle leaf spring extending from a first end to a second end; and atension shackle pivotably coupled to the vehicle frame about an axis,the tension shackle defining a channel, the second end of the leafspring disposed within the channel of the tension shackle, whereinpivoting of the tension shackle in response to an increasing, upwardload reduces the effective length of the leaf spring.
 9. The system ofclaim 8, further comprising an eye spring bushing coupled to the vehicleframe, the first end of the leaf spring coupled to the eye springbushing.
 10. The system of claim 9, further comprising a bumperoperatively coupled to, or integrally formed with, the eye springbushing and disposed between the eye spring bushing and the vehicleframe, the bumper spaced from the vehicle frame in a first condition ofthe leaf spring and configured to provide a first spring rate, and incontact with the vehicle frame in a second condition of the leaf spring,contact between the bumper and the vehicle frame configured to provide asecond spring rate of the leaf spring.
 11. The system of claim 10,wherein the bumper is formed of a polymeric material.
 12. The system ofclaim 8, further comprising a bumper operatively coupled to, orintegrally formed with, the first end of the leaf spring and disposedbetween the leaf spring and the vehicle frame, the bumper spaced fromthe vehicle frame in a first condition of the leaf spring and configuredto provide a first spring rate, and in contact with the vehicle frame ina second condition of the leaf spring, contact between the bumper andthe vehicle frame configured to provide a second spring rate of the leafspring.
 13. The system of claim 8, wherein the single leaf spring isformed of a composite material.
 14. The system of claim 8, wherein thesingle leaf spring is formed of metal.
 15. A variable rate leaf springvehicle suspension system comprising: a vehicle frame; a first leafspring extending from a first end to a second end; a second leaf springextending from a third end to a fourth end; a tension shackle pivotablycoupled to the vehicle frame about an axis, the tension shackle defininga channel, the second end of the first leaf spring disposed within thechannel of the tension shackle, wherein the axis about which the tensionshackle is pivotable is below the second end of the first leaf spring; afirst bumper disposed between a top surface of the first leaf spring andthe vehicle frame; and a second bumper disposed between a top surface ofthe second leaf spring and a bottom surface of the first leaf spring,the second bumper spaced from the first leaf spring in a first loadcondition of the second leaf spring and configured to provide a firstoverall spring rate, and in contact with the first leaf spring in a loadsecond condition of the second leaf spring, contact between the secondbumper and the first leaf spring configured to provide a second overallspring rate, the first bumper spaced from the vehicle frame in a thirdload condition of the second leaf spring and configured to provide athird overall spring rate, and in contact with the vehicle frame in afourth load condition of the second leaf spring, contact between thefirst bumper and the vehicle frame configured to provide a fourthoverall spring rate.
 16. The system of claim 15, further comprising aneye spring bushing coupled to the vehicle frame, the first end of thefirst leaf spring coupled to the eye spring bushing.
 17. The system ofclaim 15, wherein the first bumper and the second bumper are each formedof one or more polymeric materials.
 18. The system of claim 15, whereinthe first leaf spring and the second leaf spring are each formed of oneor more composite materials.
 19. The system of claim 15, wherein thefirst leaf spring and the second leaf spring are each formed of one ormore metals.
 20. The system of claim 15, wherein one of the first leafspring and the second leaf spring is formed of a metal and the other ofthe first leaf spring and the second leaf spring is formed of acomposite material.